1. Technical Field
The present invention relates generally to data processing networks, and more particularly to a data processing network in which a multiplicity of host processors are connected to shared resources.
2. Related Art
In many data processing networks, a large number of host processors share resources such as a database or storage subsystem. Typically, each host has a high probability of obtaining immediate access, but immediate access is not guaranteed. The cost of guaranteeing immediate access is usually considered to be much greater than the benefit to the user.
The probability of obtaining immediate access can be increased by using various techniques. A direct but rather costly solution is to provide additional network paths and additional storage resources, such as additional paths to duplicate storage servers for read-only storage volumes. Other techniques, such as dynamic routing and load balancing, attempt to use existing network and storage resources more effectively.
Dynamic routing directs each data access requests along a path that is selected in accordance with the resources that are currently available in order to avoid overload of resources in the network. Load balancing assigns alternative resources to the hosts in order to avoid overload of any one of the alternative resources by receipt of simultaneous access requests from a large number of the hosts. For dynamic routing and load balancing to be particularly effective, however, additional resources are required in order to gather intelligence about the current or expected state of the network, and to control or restrict the path of the data access requests in a fashion that is beneficial. These additional resources tend to introduce cost and complexity into the data network and often reduce performance during usual operating conditions.
In accordance with one aspect of the invention, there is provided a method for controlling access of host processors to alternative shared resources in a data network. The method includes storing in a directory a specification of a respective subset of the alternative shared resources which are accessible to each of the host processors, and operating a directory service for accessing the directory in response to a request from each host processor for reporting to each host processor a set of network addresses of the alternative shared resources for each host processor. The set of network addresses of the alternative shared resources for each host processor including only the network addresses of the alternative shared resources in the respective subset of the alternative shared resources which are accessible to each host processor. The method further includes operating each host processor including each host processor sending a request to the directory service for a report of network addresses of the alternative shared resources, and receiving from the directory service a report of the set of network addresses of the alternative shared resources for the host processor; and then the host processor commencing a sequence of data processing operations during which the host processor transmits service requests to at least one network address in the set of network addresses of the alternative shared resources for the host processor.
In accordance with another aspect of the invention, there is provided a method of controlling access of host processors to ports of a storage subsystem in a data network including a switch linking the host processors to the ports of the storage subsystem. The method includes storing in a directory a specification of a respective subset of the ports of the storage subsystem which are accessible to each of the host processors, and operating a directory service for accessing the directory and for reporting to each host processor the respective subset of the ports of the storage subsystem which are accessible to the host processor. The method further includes operating each host processor including each host processor sending a request to the directory service for a report of the respective subset of ports of the storage subsystem which are accessible to the host processor; and receiving from the directory service a report of the subset of the ports of the storage subsystem which are accessible to the host processor. Then the host processor commences a sequence of data processing operations during which the host processor transmits storage access requests to at least one port included in the respective subset of ports of the storage subsystem which are accessible to the host processor.
In accordance with another aspect of the invention, there is provided a digital computer programmed to providing a directory service in a data network. The digital computer is programmed with a configuration database of information about host processors in the network and shared resources in the network that are accessible to the host processors. The configuration database further includes information specifying, for each host processor, a respective subset of the shared resources which are accessible to the host processor. The digital computer is programmed to respond to a request from each host processor for information about resources in the network by reporting to the host processor information about the respective subset of the shared resources that are accessible to the host processor, thereby selectively restricting access of the host processors to the shared resources.
In accordance with yet another aspect of the invention, there is provided a machine readable program storage device containing a program for programming a digital computer to providing a directory service in a data network. The directory service accesses a configuration database of information about host processors in the network and shared resources in the network and information specifying for each host processor a respective subset of the shared resources which are accessible to the host processor. The directory service responds to a request from each host processor for information about resources in the network by reporting to each host processor information about the subset of the shared resources that are accessible to the host processor, thereby selectively restricting access of the host processors to the shared resources.
In accordance with still another aspect of the invention, there is provided a storage network that includes a cached storage subsystem and a switch for routing data access requests from a plurality of host processors to the cached storage subsystem. The cached storage subsystem includes a plurality of storage devices, a cache memory linked to the storage devices for filling the cache with data from the storage devices, and a plurality of port adapters providing storage ports for access to the cache memory. The switch has a plurality of network ports and is linked to the storage ports for selectively routing data access requests from the network ports to the storage ports. The network ports are connectable for receiving the data access requests from a plurality of host processors. The storage network further includes a digital computer programmed with a configuration database of information about the host processors and the storage ports. The configuration database further includes information specifying, for each host processor, a respective subset of the storage ports which are accessible to the host processor. The digital computer is programmed to respond to a request from each host processor for information about the storage ports by reporting to the host processor information about the respective subset of the storage ports which are accessible to the host processor , and thereby selectively restrict access of the host processors to the storage ports.